Adverse biological effects resulting from exposure to extremely low frequently (ELF) electric fields (EF) have been claimed. There is strong evidence that the EF-induced membrane potential is involved in induction of these effects. Plant roots provide a model cell system in which ELF-EF effects are observed; growth inhibition is correlated with EF-induced membrane potential magnitude. Study of roots from two species indicates a threshold at EF-induced membrane potential 3 mV; at EF-induced membrane potential 10 mV, growth nearly ceases. The project will explore a possible mechanism by which EF- induced membrane potential are transduced into growth effects. Mediated H+ efflux from plant cells is involved in cellular growth. The effect of ELF-EF exposure on H+ efflux will be studied, and will provide a basis for comparison of EF effects on ion transport in roots and erythrocytes, in which EF-induced membrane potential affect Na/K transport. The project will also quantify the relationship between EF-induced membrane potential and growth effect magnitude in roots of several genera, assess interspecific differences, and test a general model of the relationship. Exposure conditions likely to induce comparable EF- induced membrane potential in other systems will be calculable. The effect of ELF-EF exposure on H+ efflux from roots will be examined by measuring the rate at which EF-exposed and sham- exposed root tip suspensions acidify a weakly-buffered suspension fluid; it is hypothesized that EF exposures which inhibit root growth will inhibit or reverse H+ efflux from the roots. A dose- response relationship will be sought for any such effect observed, and the results related to the mean EF-induced membrane potential in the root tips. The relationship between EF-induced membrane potential and growth effect magnitude will be examined in roots of 4 species by measuring the growth rates of marked segments within the elongation zone following ELF-EF exposure/sham-exposure onset at various EF strengths. Segmental growth rates will be related to the mean EF-induced membrane potential in the segment, the latter calculated on the basis of the applied EF strength and the mean size of cells in the segment. Cell size data will be obtained from serial histological sections.